Simply put they are the ones who imagine and create The vary world around them. Kinda God like you might say.

[Edit]And they both poses a epic and exclusive to them set.

Cherub's set.
Front
Back
Left
Right

Boswick's set.
Front

On a further note if any of this content is spoilers please remove it. I no wants to be a is party pooper.

[Edit]I heard that once Boswick And The Cherub Fought against each other in Old Beta PvP, But after they destroyed half of Cradle {Fortunately for us it was not the half we where on} And Nick had to fix it They where permanently ban from playing SK ever again.

And to keep such from happening ever again Nick sealed Boswick's character in a bush and Placed it at the Core to power the clockworks.
As for the cherub's character It was split in to 1,000 parts Witch took form and became the Snipes.
An that kids is why you never see The Cherub or Boswick playing SK.

[Edit]@Tengu No no no. You got it all wrong, Cherub isn't the swarm he is the swarm's creator and master. And I still don't know why Boswick got such a bad rep. After all it is Cherub that creates all the frustrating and Tear Induseing Things in SK. Cherub is responsible for horrors like Gremlins, Fiends, Spookats, Slimes and Any thing else that made us cry. Tho Cherub might not be so bad if he Slept once in awhile.